At the end of the Second World War, huge volumes of unexploded munitions were deliberately sunk off the coast of Germany in the south-west Baltic Sea.
These dumping sites have remained on the seabed for the past 80 years, during which time scientists have used underwater robots to map their location.
However, as these old munitions corrode, harmful chemicals are spreading beyond the original dumping zones. This contamination is expected to worsen over time, posing an increasing risk to marine life. Climate change is adding to the problem, with rising sea temperatures and stronger storms accelerating the release of toxic substances.
To find out more about the extent to which these chemicals are spreading, researchers from GEOMAR Helmholtz Centre for Ocean Research Kiel conducted a study using water samples taken from the area.
Their findings, published in the journal Chemosphere, confirm that "traces of ammunition-related chemicals were found in almost every sample", in some cases in concentrations approaching critical levels.
So, what does this mean for marine life and the environment?
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Toxic chemicals detected in the water
In 2017 and 2018, researchers collected water samples from the Bay of Kiel, the Bay of Lübeck and other sites around the 'unexploded ordnance' – more commonly known as UXO.
They then analysed the samples – looking specifically at MCs, or microcystins (a group of toxins produced by certain types of cyanobacteria), suspended particles and sediments.
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Researchers found traces of ammunition-related chemicals in almost every sample. Although most concentrations were below harmful levels for marine life and drinking water standards, some came close to critical thresholds.
"Unexploded ordnance contains toxic substances such as TNT (2,4,6-trinitrotoluene), RDX (1,3,5-trinitro-1,3,5-triazine), and DNB (1,3-dinitrobenzene), which are released into the seawater when the metal casings corrode,” explains lead author Dr Aaron Beck, a geochemist at GEOMAR.
The study found "measurable levels" of these toxins in a variety of algae, invertebrates and fish in the south-west Baltic Sea.
"These compounds pose a threat to the marine environment and living organisms as they are toxic and carcinogenic,” says Dr Beck.
Researchers estimate that around 3,000 kilograms of toxic munitions chemicals are currently dissolved in the region’s waters. Without intervention, this number is expected to rise as the metal casings continue to corrode – potentially for another 800 years.
Different regions, different risks
The study found that contamination levels vary depending on the types of munitions dumped in each area.
The Bay of Kiel showed particularly high concentrations of TNT, while the Bay of Lübeck had higher levels of RDX and DNB. Most of these chemicals were dissolved in the water rather than attached to sediments or particles.
A global concern
The authors of the study point out that it's not only marine life that feels the effects of the unexploded munitions: "Underwater munition removal is increasingly necessary to allow sediment dredging and offshore infrastructure development including aquaculture, wind farms, power and communication cables, and pipelines."
The issue of legacy munitions pollution is not limited to the Baltic Sea. Similar problems exist worldwide, and the researchers are calling for dumped ordnance to be recognised as “historical contaminants of emerging concern”.
"Unlike diffuse pollution sources, UXO exists in a concentrated, already packaged form. This means it can be physically removed from the environment," says Dr Beck, adding that Germany’s approach to munitions clearance could serve as a model for other countries dealing with similar problems.
"With war relics, at least one environmental stressor can be permanently eliminated from the marine ecosystem.”
Germany’s munitions clearance pilot project
The German government has launched a €100 million pilot project to recover and safely dispose of these hazardous remnants of war. This is the world’s first dedicated effort to clear underwater munitions on a large scale.
The operation began in autumn 2024 in the Bay of Lübeck, and researchers are now using the data collected to develop an autonomous clearance system. This cutting-edge technology aims to treat and incinerate the unexploded munitions at sea, preventing further contamination and protecting marine life for generations to come.
Main image: Unfired sea mine in Kolberger Heide/GEOMAR Helmholtz Centre for Ocean Research Kiel
Find out more about the study: Widespread environmental contamination from relic munitions in the southwestern Baltic Sea
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